This invention relates generally to resonant cavities and more particularly to temperature compensated tunable resonant cavities.
An RE resonant cavity (or multiple interconnected cavities) can be used to create a RF filter. The filter may either pass a RF signal over a limited frequency range (a bandpass filter) or exclude an RF signal over a limited frequency range (a notch or bandstop filter), depending upon how the resonator is connected to the overall system. A perfect single cavity device would operate at a single, specific frequency (the resonant frequency), however due to material and other considerations all resonant frequency devices operate over a frequency range which encompasses the resonant frequency. Usually, it is desired to pass energy over a broad band of frequencies while blocking energy above and below this frequency range. This is achieved by combining or coupling multiple cavities. This causes the frequency response curve to widen. In addition, multiple filters with separate resonant frequencies can be connected together to form a duplexer. A duplexer is a device with, for example, two filters operating at different resonant frequencies and having one output in common.
A single-cavity RF resonator for use either individually or as part of an array of cavities is realized by having a conductive inner conductor or post within an enclosed conductive cavity. The post is connected to the housing at one end and extends towards die top of the cavity. The conductive cavity is formed within a conductive housing and enclosed by a conductive lid. The resonant frequency of the cavity is selected by adjusting the length of the post. Prior art systems for adjusting the length of the post have been relatively complex. In addition, in order to realize a system that is stable over temperature variations it is necessary to minimize the change in resonant frequency with respect to thermal variations of die system.
It is an object of the present invention to provide a resonant cavity of the type having a conductive post with an improved adjustment mechanism.
It is another object of the present invention to provide a temperature compensated tunable resonant cavity.
The foregoing and other objects of the invention arc achieved by a tunable cavity which includes a conductive post assembly comprising a post extending upwardly from the bottom wall, a bellows having one end secured to die top of the post, a top secured to the other end of the bellows, said top including an internal thread, and an adjustment screw extending upwardly from the bottom and threaded into said top. A spring is disposed between the top of the post and the top serving to urge them apart and to securely seat the adjustment screw.